The present invention relates to a rod-fed electron beam evaporation system in which a rod-like ingot is fed into a crucible of an electron beam evaporation source. More particularly, the present invention relates to such a system in which the ingot and a replacement ingot self-engage in an in-line relationship so that the ingot and replacement ingot can be urged upwardly into position within the crucible of the electron beam evaporation source.
In physical vapor deposition by electron beam evaporation, an evaporant is evaporated within a crucible to produce a vapor cloud which acts as a transport media to deposit the evaporant on a substrate. In a rod-fed electron beam evaporation source, the evaporant in the form of a rod-like ingot is upwardly fed into a central opening provided within a crucible. The ingot is evaporated within the crucible by an electron beam deflected through an arc of 270.degree.. The ingot and replacement ingots are contained within a rotating magazine located within a vacuum chamber in which the electron beam evaporation source operates. Before each ingot has been spent, the ingot is held in position while a replacement ingot from the rotary magazine is aligned with the ingot being held. An ingot pusher pushes the replacement ingot in an upward direction, against the held ingot, to continue to raise the ingot being evaporated and the replacement ingot into the crucible. The ingot pusher is acted upon by a pusher platform which is raised and lowered by a ball screw mechanism.
Within the electron beam evaporation source, a permanent magnet and pole pieces are provided to produce the magnetic field that is used in deflecting the electron beam through the 270.degree. arc. An electron beam gun used to produce the electron beam is situated opposite to the magnet and spaced therefrom to allow for passage of the ingot to the crucible. Even though electron beam evaporation sources are cooled by cooling water, the heat generated by the melting and evaporating ingot is conducted down the ingot to below the water cooled portion and then radiated to the crucible, to the pole pieces, permanent magnet and electron beam gun. Thus, the use of rod-fed electron beam evaporation sources has been limited to materials which melt at relatively low temperatures, for instance aluminum. Higher melting evaporants such as molybdenum have not been used in rod fed sources due to the high melting temperature of such materials and therefore, the high heat conduction to components of the electron beam evaporation source.
In order for a magazine fed electron beam evaporation source to properly function, there must be a great deal of precision in the fabrication and operation of the feed mechanism so that the replacement ingot is in perfect alignment with the ingot being evaporated. Additionally, there is a certain degree of complexity in such equipment in that not only must a rotating magazine and ingot pushing mechanism be provided but also a mechanism to hold the ingot during alignment of the replacement ingot. Such precise tooling and mechanical complexity translates into a large part of the fabrication costs of such an electron beam evaporation source.
As will be discussed, the present invention provides an electron beam evaporation system that does not require the same degree of mechanical precision and complexity as prior art rod-fed systems. Moreover, the system of the present invention is capable of evaporating ingots composed of materials having higher melting temperatures than materials of the prior art.